Unset the number string in the zero filled number list
Unset the number string in the zero filled number list

This is necessary because the wrong `index` will be selected if a 
submitted number has identical groups.

For example 123123 would be converted to [‘123’,’123] and getting the
index for ‘123’ would always return 0 if the first item wasn’t set to 
None once it had been processed.
ianfieldhouse/number_to_words